Performance of the NSSL Experimental Warn-on-Forecast System for Ensembles (NEWS-e) during VORTEX-Southeast

The goal of the National Oceanic and Atmospheric Administration’s Warn-on-Forecast project is to produce probabilistic, short-term O(1 hr) guidance for severe thunderstorm hazards in the United States.  Working towards this goal, NSSL and the Global Systems Division (GSD) have developed a prototype WRF- and EnKF-based ensemble storm-scale prediction system, which has been run during the winter and spring of 2016.  This system produces twice-hourly updates of 90-min forecasts with 3-km horizontal grid spacing using the 36-member NEWS-e, which is initialized using GSD’s 3-km, experimental High-Resolution Rapid Refresh Ensemble (HRRRE). 

NEWS-e forecasts have regularly produced accurate forecasts of low-level rotation well in advance (>30 min) of tornado development for discrete supercells within highly favorable tornado environments.  However, less is known about NEWS-e forecast performance in more marginal environments typical of cool season tornadoes in the southeastern U.S.  This study examines NEWS-e thunderstorm rotation forecasts for four cool season events in 2015-2016, including for VORTEX-SE intensive operating periods on 31 March and 29 April 2016. 

Each NEWS-e low-level vertical vorticity and updraft helicity forecast is verified against Multi-Radar Multi-Sensor azimuthal wind shear values from the WSR-88D network using an object-based approach.  Additionally, the upstream environment of each forecast rotation object will be extracted from NEWS-e.  This approach allows both storm-scale (e.g. storm size, cold pool interaction) and mesoscale (e.g. conditional instability, vertical wind shear) impacts on forecast accuracy to be assessed across the four cases.